In general, alkaline batteries have a structure in which an opening of a battery case is sealed using a resin sealing member and a negative electrode terminal plate. Specifically, they have a structure in which a sealing member is interposed between a battery case and a negative electrode terminal plate, and the end portion of the opening of the battery case is curved inward, and then crimped toward the periphery of the terminal plate with the sealing member interposed therebetween, so that the terminal plate is fixed tightly. Various studies have been carried out with respect to the sealing member used in a sealing portion of alkaline batteries.
For example, Patent Document 1 proposes that in coin type batteries, the moisture rate in a sealing member made of 6,6-nylon be adjusted to as low as 0.5 to 2.0%, thereby to enhance the mechanical strength of the sealing member and improve the leakage resistance. Moreover, Patent Document 2 proposes that in coin type batteries, for a sealing member, 6,12-nylon whose water absorption rate is low, dimensional change is small, and tensile strength is high be used, thereby to improve leakage resistance.
Among alkaline batteries, there is a battery having the following structure. The battery includes a battery case also serving as a positive electrode terminal for housing a power generating element in the interior thereof, and an assembled sealing part for closing an opening of the battery case. The assembled sealing part comprises: a negative electrode terminal plate; a negative electrode current collector having a head for providing an electrical connection with the negative electrode terminal plate, and a shank; and a resin sealing member. The sealing member comprises a central cylindrical portion having a through-hole for inserting the shank of the negative electrode current collector therethrough, a peripheral cylindrical portion interposed between the periphery of the negative electrode terminal plate and the end portion of the opening of the battery case, and a joint portion for joining the central cylindrical portion and the peripheral cylindrical portion. The end portion of the opening of the battery case is curved such that the top of the peripheral cylindrical portion of the sealing member is wrapped therein, and the curved portion is crimped inward, so that the periphery of the negative electrode terminal plate is fixed tightly.
However, in the alkaline batteries having the aforementioned structure, even in the case where the techniques as proposed in Patent Documents 1 and 2 are applied, if the batteries are stored in a high humid environment, the moisture rate in the sealing member is increased, and a creeping phenomenon easily occurs between the negative electrode current collector and the sealing member, making it difficult to surely prevent the leakage. The creeping phenomenon occurs when the reactions as expressed in the formula (1) and the formula (2) below are facilitated between the negative electrode current collector and the sealing member as a result of the increase in the moisture rate in the sealing member.O2+H2O+e−→4OH−  (1)2H2O+2e−→2OH−+H2  (2)
In particular, in the case where nickel oxyhydroxide is used for the positive electrode active material in order to improve the heavy load discharge characteristics as in the case of Patent Document 3, the positive electrode potential is high, and thus the amount of oxygen gas generated by the electrolysis of water is increased. When oxygen is present as in the case of Non-Patent Document 1, the reaction as expressed by the formula (1) proceeds on the surface of the negative electrode current collector, and thus the creeping as mentioned above is facilitated. For the reasons above, in the case of using nickel oxyhydroxide for the positive electrode active material, compared with the case of using manganese dioxide, disadvantageously, the leakage resistance is easily reduced.
Patent Document 1: Japanese Laid-Open Patent Publication No. Sho 60-56360
Patent Document 2: Japanese Laid-Open Patent Publication No. Sho 60-77352
Patent Document 3: Japanese Laid-Open Patent Publication No. Sho 57-72266
Non-Patent Document 1: J. Electrochem. Soc., Vol. 124, (1977), P332